Biology 11 Kingdom Animalia Phylum Mollusca: The Soft Bodies

Phylum Mollusca Objectives State why Molluscs are more advanced than Nematods Describe the 3 defining characteristics of Molluscs Describe the 7 Classes and example animals Know squid anatomy

Phylum Mollusca Mollusca = soft bodies Second largest phylum of animals Characteristics: Three defining traits: 1. Large ventral muscular foot 2. Visceral mass located dorsal to the foot 3. Tissue layer called “mantle” covers the visceral mass

Phylum Mollusca Evolution Likely a similar ancestor as annelids, due to: 1. Same type of larvae (Trochophore Larvae) 2. Evidence of segmentation seen in larvae and primitive members of this phylum

Class Monoplacophora (AKA: one plate) The first mollusk, now considered a living fossil: thought to be extinct until one was found in Costa Rica in the mid 1950s Looks like a limpet but found in the deep ocean.

Class Polyplacophora (AKA: many plated) The Chitons Exclusively marine Have 8 dorsal plates Primitive with segmentation have radula scrapers to feed on algae

Class Aplacophora (AKA: naked molluscs) Lack a shell, secrete calcium-based spicules instead and appear shiny worm-like animals found deep in the ocean

Class Gastropoda (AKA: stomach foot) Largest class. May or may not have a shell (slugs) Live in fresh, salt water, and land Contains single spiral shell Well developed senses Snails, slugs & nudibranchs Nudibranch Banana Slug

Gastropoda torsion: rotation of digestive system

The Radula

Class Scaphopoda (AKA: shovel foot) Live burrowed in the marine mud, head down Tusk shaped shell is open at both ends (unique!!) Ex animal: tusk shelled organisms

Class Bivalvia (AKA: 2 shells) Contain 2 hinged shells (valves) Filter feeders, sessile Use gills for respiration & filter feeding Includes: clams, oysters, scallops, mussels Clams Mussels

Class Cephalopoda (AKA: head foot) Octopus These are the most highly evolved invertebrates Have vertebrate eye (parallel evolution) Capable of learning Very motile predators - largest invertebrate Shell greatly reduced Squid

The cuttlefish and nautilus Class Cephalopoda The cuttlefish and nautilus Cuttlefish

Clam re-section diagram: